Digital music players have become ubiquitous. Such players, also referred to as portable media players (PMP) or digital audio players (DAP), are consumer electronics devices that store and play digital media such as audio, images, video, documents, and the like. A non-limiting example is the iPod® brand of portable media players created and marketed by Apple Inc., Cupertino, Calif., U.S.A. Other types of electronic devices like cellphones, internet tablets, and digital cameras are sometimes referred as PMPs because of their playback capabilities. Furthermore, personal computers are typically equipped with software which permits playing digital media, such as Windows Media Player® available from Microsoft Corporation, Redmond, Wash., U.S.A., and iTunes® software available from Apple Inc.
The “Genius” feature of Apple's iTunes software automatically generates a playlist of songs from a user's library which are similar to a selected song, making use of a ratings system and collaborative filtering.
Pandora® Internet Radio is an automated music recommendation service. The service plays musical selections similar to song suggestions entered by a user. The user provides positive or negative feedback for songs chosen by the service, which are taken into account for future selections. While listening, users are offered the ability to buy the songs or albums at various online retailers.